1. Field of the Invention
The present invention relates to a rotation angle detecting device that detects a rotation angle of a rotary object.
2. Description of the Related Art
JP-B2-2842482 or either one of its counterpart U.S. Pat. Nos. 5,228,139, 5,789,917 and 6,043,645 discloses, as shown in FIG. 12, a rotation angle detecting device 100 that includes a cylindrical permanent magnet 101 to be fixed to a rotary object, a cylindrical yoke 102 and a hall element 103 disposed in one of circumferential gaps 102a, 102b. The cylindrical permanent magnet 101 is coaxially disposed within the cylindrical yoke 102 to provide a magnetic flux that changes as a rotary object rotates, and the hall element 103 provides a voltage signal that corresponds to flux density of the magnetic flux.
However, such a rotation angle detecting device can not detect an accurate rotation angle of a rotary object because such an coaxially disposed cylindrical permanent magnet can not provide a magnetic flux curve that does not have a flat portion with respect to the rotation angle, as shown in FIG. 13.